The long range goals of this project are to determine whether the vaccination of HIV-1-seronegative and seropositive human volunteers with candidate AIDS vaccines results in the generation of HIV-1-specific cytolytic T lymphocyte (CTL) responses, to analyze individual variation in the strength and duration of vaccine-induced CTL responses, and to examine important functional aspects of the CTL response at clonal level. We have previously shown that seronegative volunteers immunized with HIV-1 envelope protein subunit vaccines develop CD4+, MHC class II-restricted CTL that lyse HIV-1-infected cells in rapid, efficient, and highly specific fashion. In addition, we have recently found that individuals vaccinated with live vaccinia virus carrying the HIV-1 env gene have an extremely high level of CD8+, class I-restricted CTL activity specific for the HIV-1 envelope protein. In the proposed studies, both MHC class I- and class II-restricted CTL responses will be analyzed in human volunteers participating in all current and future NIAID-sponsored Phase I AIDS vaccine clinical trials. Assays to detect both active circulating CTL and resting memory CTL will be used. We will compare the ability of various vaccines to induce class I- and class II- restricted CTL and determine the duration of the memory response for each type of CTL. HIV-1-specific CTL clones will be isolated from vaccine recipients at multiple time points during the trials. The availability of stable, long term T cell clones will permit us to characterize in detail important parameters of vaccine-induced CTL response including phenotype, HLA restriction, epitopes recognized, cross-reactivity with various strains, and cytokines produced. Studies with CTL clones will focus on properties likely to influence ability of vaccine-induced clones to control the spread of HIV-1 infection in vivo such as capacity to lyse HIV-1-infected cells and secretion of cytokines such as TNF-alpha that upregulate HIV-1 gene expression. Finally, because class II-restricted CTL may play an important role in vaccine- induced immune response by virtue of their ability to destroy infected cells and to downregulate specific antibody responses, we will attempt to define molecular markers for the subset of CD4+ T cells with cytolytic activity and to analyze key aspects of the CD4+ CTL response, including the ontogeny of CD4+ CTL, the antigen receptor repertoire of these cells, their trafficking patterns, their role in regulation of B cell responses, and mechanism of cytolysis by these CTL.